The present invention relates to the field of internal gear pumps for lubricating oil or the like, such as are suitable for use as lubricating pumps for internal combustion engines, and in particular to such an internal gear pump which has an improved intake plenum structure.
In the field of internal gear pumps for use as lubricating oil pumps or the like, there is a known type of pump which has: a pump housing formed with a cylindrical rotor receiving cavity; an outer rotor formed with a generally cylindrical outer surface which fits closely and coaxially in the cylindrical surface of the rotor receiving cavity and is rotatable therein around their mutual central axis within the pump housing, and further has an inner cavity the defining surface of which is formed with a plurality of internal teeth; and an inner rotor somewhat smaller than said inner cavity and fitted in it towards one side thereof, which is formed with a plurality of external teeth which mesh and cooperate with said internal teeth of said outer rotor. Thereby, a pumping chamber is defined between the outer surface of the inner rotor and the inner surface of the outer rotor, i.e. between the respective teeth and thereof. These teeth may be of trochoidal shape, or of involute or hypocycloid configuration. And, with regard to the porting structure of a conventional such pump, it is per se known for an aperture formed in the pump housing to define an intake plenum and to define an intake port by opening through a portion of the circumferential wall of the rotor receiving cavity and through a corresponding portion of the bottom thereof, thus opening to the pumping chamber. And, similarly, another aperture formed in the pump housing typically defines an output plenum, and defines an output port by opening through a portion of the circumferential wall of the rotor receiving cavity and through a corresponding portion of the bottom thereof, thus also opening to the pumping chamber.
When it is desired to improve the efficiency of such a pump, it is considered to be effective to increase the size of the intake port, i.e. to decrease its flow resistance, and to this end increasing the cross sectional area of the intake port is effective. However, if the size of the intake port is increased by increasing its depth, the problem arises in such a case that the axial dimension, i.e. the thickness, of the pump is unduly increased; while, on the other hand, if the size of the intake port is increased by increasing its width, the problem arises in such a case that the circumferential wall of the rotor receiving cavity is cut away over a large and localized area, thus creating the danger that the outer rotor may not be satisfactorily rotationally supported in said rotor receiving cavity by said circumferential wall thereof.